1. Field of the Invention
The present invention relates to a lift control apparatus for a ground work apparatus which is coupled to a vehicle body of a traveling work vehicle via a lift mechanism.
2. Description of Related Art
An agricultural tractor, as one example of the traveling work vehicles mentioned above, is equipped with a lift operation lever to arbitrarily set a lift position of the ground work apparatus, and with a control apparatus to lift/lower the ground work apparatus via the lift mechanism to a lift position being set by the lift operation lever. In addition, an upper limit positioner is included to set an upper limit position of the ground work apparatus, and the control apparatus controls the lift mechanism so as not to exceed the upper limit position of the ground work apparatus regardless of the lift position being set by the lift operation lever.
In such a control apparatus mentioned above, when a worker inadvertently operates an upper limit setter after the engine is stopped, and the upper limit position becomes lower than the height of the ground work apparatus defined by the actual lift arm position, there is a possibility of the ground work apparatus being lowered to the upper limit position at a time the engine is started. Therefore, the lift control apparatus in Japanese Patent Laid-Open Publication H9-9716 includes a function preventing the ground work apparatus from being lowered to the upper limit position, when the position of the ground work apparatus, defined by the lift arm position of the lift mechanism, is higher than the upper limit position being set by the upper limit positioner at the time the engine is started. The function prevents the ground work apparatus from being lowered even though the position of the ground work apparatus is higher than the upper limit position at the time the engine is started.
It is uncommon for an operator to suddenly adjust a height of a ground work apparatus before the engine is started. However, a necessity of adjusting an upper limit of the ground work apparatus occurs frequently during working/traveling. There is a circumstance that control functions with respect to a lift mechanism stop during working/traveling, when the operator resets the upper limit (of the ground work apparatus) to a downward side and the upper limit being set is lower than the actual height of the ground work apparatus, according to a technology of Japanese Patent Laid-Open Publication H9-9716.